I have a 1988 manual 4x4 townace with a 2CT engine and viscous fan. My question is that when i start the bus in the mornings i noticed that the rev counter needle is on about 750-770rpm (cold engine) until the idel up is engaged, and when bus is at normal temp it will stay at about 800rpm. When i leave the bus for about 10-20mins (after a long run) and start the engine (still hot), the rev counter will read about the same as befor (750-770rpm). To get it at 800rpm i have to just lightly tap the accelerator and the revs will go back to 800rpm. Apart from that the bus is pretty much perfect. When i first got the bus it was reading about 800rpm all the time (except when the idle up is engaged). Can anyone shed some light as to what may be the problem. I understand that the RPM should be between 750-850rpm and the bus is still within specifications.

- (#6018) Graham, 5 Nov 02

I'm not as au fait with diesels as some of the other learned contributers to this site so can't give a technical reason for the change in idle speed but I don't see as you have a problem. Mine does the same depending upon engine temperature. You could try altering the idle screw but as yours is within recommended tolerance I would leave well alone.

- (#6044) Ian Dunse, 6 Nov 02

Idle is affected by all sorts of issues- oil temp, coolant temp, fuel temp, air temp. Also fuel quality and filter conditions, and alternator load. Never mind anything else, are you sure the speed is actually changing, OEM tachos aren't the most reliable things ever...
There might be a degree of play in one of the many parts of the governor, but whatever, I wouldn't worry about it. If you want truly stable idle, buy a VW TDI- they vary the injection quantity for each individual cylinder to stabilise and smooth idle!

- (#6045) david miller, 7 Nov 02

My idle up switch doesn't appear to anything. I quizzed this with a mechanic friend of mine. He informed that unless your revs drop quite a bit, the idle up switch has nothing to do so does nothing. At 750rpm it still shouldn't have anything to do.

David, regarding your VW TDI story, if you mean the water cooled variety from the van, I'd agree it ticks over quite well but they are renowned for eating cylinder heads at 100,000 miles. The problem doesn't seem to effect the old air cooled units.

- (#6046) Dave Brandwood, 7 Nov 02

Dave, I'm talking about the electronically injected, but pre- pumpe deuse 1900 as used in Golf, Pasaat, T4 etc.You're thinking of the 1.6- 1.9l IDI engine.
The idle up switch only has an effect if the heater fan is on (that's where it's supply comes from) Should give 1000rpm or so.

- (#6047) david miller, 7 Nov 02

Thanks For The quick Response From everyone but the problem i have with the idle speed is now worse. It is now hard to start the engine. When the engine is going the idle is very rough. I would have to rev the engine to either get it to start or smooth out the idle (or both). This problem happens only when engine is cold. Apart from that the engine will preform really well. I have checked the glowplugs and they seem to be operating within normal spec's.

- (#6048) Graham, 7 Nov 02

Sounds like a problem with the pump- possibly just an air leak. Check for leaks, and check especially the maximum fuel screw- it's above the injection pipes at the rear of the pump. If that's loose (A locknut secures it) it would cause all the above problems.
Also check the idle up assy on the side of the pump for freedom, stick a touch of oil on it's pivots.

If the fuel screw is slack, don't turn it too much- get the engine hot, and turn it to give the reccomended idle speed. The stand on the throttle and check the maximum governed speed is NO MORE THAN 5100rpm. Make fine adjustments to get both right.
(or take it to a specialist- too much fuel will burn holes in your pistons!)

- (#6049) david miller, 8 Nov 02